Multi-layer information recording medium and information recording and reproducing apparatus

ABSTRACT

A multi-layer-information-recording medium is applied to an information recording and reproducing apparatus capable of recording or reproducing information on and from either of a single-layer-information-recording medium having a single recording layer on one side, and a multi-layer-information-recording layer having a plurality of recording layers layered on a spacer layer on one side as a change in reflectivity by irradiating a light beam. The multi-layer-information-recording medium is compatible in terms of at least reproducing and recording with a single-layer-information-recording medium having a cover layer having a predetermined refractive index “n” and a thickness “t” disposed on a recording layer on a light incident side surface. The multi-layer-information-recording medium includes a deepest recording layer deepest from the light incident side surface. The deepest recording layer is formed at an optical distance d 1  from the light incident side surface satisfying an equation d 1 =nt. The multi-layer-information-recording medium also includes at least one shallow recording layer formed at an optical distance d 2  satisfying an inequality d 2 &lt;nt from the light incident side surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a reissue application of U.S. Pat. No. 6,773,781 B2,which issued on Aug. 10, 2004, from U.S. patent application Ser. No.10/147,979, filed on May 20, 2002, the entirety of which is incorporatedherein by reference. This application claims the benefits of priorityunder 35 U.S.C. § 119, 120 to Japanese Patent Application No. 2001 -156477, which was filed in the Japanese Patent Office on May 25, 2001,the entirety of which is incorporated herein by reference. Other relatedreissue applications claiming priority to this reissue applicationinclude U.S. Reissue patent application Ser. No. 11/200,543, filed Aug.10, 2005, now pending; U.S. Reissue patent application Ser. No.11/200,544, filed Aug 10, 2005, now pending; and U.S. Reissue patentapplication Ser. No. 11/200,545, filed Aug. 10, 2005, now pending.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an information recordingmedium such as an optical disc, an optical card and the like, and moreparticularly to a multi-layer-information-recording medium which has aplurality of recording layers layered on spacer layers.

2. Description of the Related Art

In recent years, optical discs are widely used as means for recordingand reproducing data such as video data, audio data, computer data andthe like. A high density recording disc called DVD (Digital VersatileDisc) has been used in practice. As one type of DVD, there is amulti-layer disc in a laminate structure which has a plurality ofrecording layers that can be read from one side of the disc. A two-layerdisc having two recording layers on one side has been used in practiceas a disc dedicated to reproduction.

As illustrated in FIG. 1, the two-layer DVD dedicated to reproductioncomprises a shallow recording layer, which is the first layer viewedfrom the side on which data is read, i.e., closer to a light incidentside surface, and a deep or second recording layer. With the two-layerdisc, any signal recorded in the shallow recording layer and the deeprecording layer can be read from one side of the disc only by moving thefocus of a reproducing light beam. The shallow recording layer is madeof a translucent film such that a light beam can transmit the shallowrecording layer and read a signal from the deep recording layer, and thefilm thickness and material are chosen conveniently for the shallowrecording layer. A reflective film is used for the deep recording layer.An optically transparent spacer layer having a high transmittance at thewavelength of light is disposed between the shallow recording layer andthe deep recording layer in order to separate these layers by a constantdistance.

The DVD standard defines that a transparent cover layer on a recordinglayer of a single-layer disc, having only one recording layer, 600 μmthick, as illustrated in FIG. 2. On the other hand, a two-layer disc isformed to have a first recording layer and a second recording layerpositioned at depths of 570 μm and 630 μm from the surface on which alight beam is incident, i.e., above and below the depth of 600 μm atwhich the recording layer of a single-layer DVD is disposed. Thepositioning of the two layers above and below the single recording layerin the thickness direction is employed in the two-layer disc because anoptical pickup system for recording and reproducing signals conformingto the DVD standard comprises an objective lens having a relativelysmall numerical aperture of 0.6 which is designed for the cover layer of600 μm thick, and even with such an objective lens having a smallnumerical aperture, a deviation of approximately 30 μm in depth of thefirst layer and the second layer each from the single recording layerdoes not significantly affect the reading of signals. In this event,though the deviation of 30 μm of the recording layers causes waveaberration in a reading light beam, the amount of wave aberration is toosmall to cause a problem when the numerical aperture is on the order of0.6.

A long program such as a movie which overflows the first recording layerof the two-layer disc is reproduced from the two recording layers. TheDVD standard also defines a single side signal-reproducing scheme,called an opposite track path scheme, for continuously reprodcuing fromtwo layers. The opposite track path scheme involves reproducing from therecording layer at a depth of 570 μm from the inner periphery to theouter periphery, jumping the focus from the outer periphery of thisrecording layer to the recording layer at a depth of 630 μm, andreproducing signals on the deeper recording layer from the outerperiphery to the inner periphery. In this event, by reading aninformation region representing the contents of the disc recorded on thelayer at a depth of 570 μm, the apparatus can sense the title of theDVD, a program duration, or the two-layer disc in accordance with theopposite track path scheme.

Meanwhile, an increasing amount of information requires a higher densityfor next-generation optical disc. It is considered that the numericalaperture of the objective lens be increased to 0.8 or more for a higherdensity. When using an objective lens having such a large numericalaperture, the amount of wave aberration caused by an error in thicknessof the cover layer on the recording layer increases too much to readsignals, thereby failing to readily reproduce a next-generation opticaldisc when it is in a two recording layer structure. It is thereforeconsidered that an optical system capable of adjusting the amount ofwave aberration should be incorporated in a pickup to make acompensation for preventing the wave aberration in accordance with thedepth of a recording layer.

When an optical system for compensating for the wave aberration is usedto read a single-layer disc and a multi-layer disc such as a two-layerdisc of the next-generation while maintaining the compatibility, thedifference exists in thickness of a cover layer corresponding to depthsbetween the respective recording layers, so that a light beam must befocused on each recording layer while correcting the same for the waveaberration to search for lead-in information and the like. This givesrise to a problem that the time taken for starting reproduction becomeslong if a two-layer disc is reproduced immediately after a single-layerdisc was reproduced. In addition, with a large numerical aperture, alarger thickness of the cover layer causes an allowable range to besignificantly narrowed down for the inclined disc, so that a multi-layerdisc which has a larger thickness of cover layer than a single-layerdisc must be fabricated with an improved planarity for the surface ofthe disc more than the single-layer disc.

OBJECT AND SUMMARY OF THE INVENTION

The present invention has been made in view of the situation asdescribed above, and it is an object of the invention to provide amulti-layer-information-recording medium which permits rapid datareproduction even when information is recorded or reproduced using anobjective lens having a large numerical aperture of 0.8 or more, andwhich can be fabricated with an equivalent planarity to a single-layerdisc, and an information recording and reproducing apparatus suitablefor use with the multi-layer-information-recording medium.

According to the present invention, there is provided amulti-layer-information-recording medium having a plurality of recordinglayers layered on a spacer layer on one side and applied to aninformation recording and reproducing apparatus capable of recording orreproducing information on a single-layer-information-recording mediumhaving a single recording layer and a cover layer on one side as achange in reflectivity by irradiating a light beam through the coverlayer onto the recording layer.

The multi-layer-information-recording medium of the present inventioncomprises:

-   -   a deepest recording layer disposed deepest from a light incident        side surface at an optical distance d1 satisfying an equation        d1=nt wherein “n” denotes a predetermined refractive index of        the cover layer of the single-layer-information-recording medium        compatible in terms of at least reproducing and recording with        said multi-layer-information-recording medium and “t” denotes a        thickness of said cover layer; and    -   at least one shallow recording layer disposed at an optical        distance d2 satisfying an inequality d2<nt from the light        incident side surface.

According to one aspect of the present invention, saidmulti-layer-information-recording medium comprises only two layersconsisting of said deepest recording layer and said shallow recordinglayer.

According to another aspect of the present invention of themulti-layer-information-recording medium, physical address informationis recorded sequentially from said shallow recording layer to saiddeepest recording layer in a shallower order from the light incidentside surface.

According to a further aspect of the present invention of themulti-layer-information-recording medium, physical address informationis sequentially recorded in order from an inner periphery to an outerperiphery of said deepest recording layer.

According to a still further aspect of the present invention of themulti-layer-information-recording medium, the physical addressinformation is sequentially recorded alternately in a forward directionfrom the inner periphery to the outer periphery and in an oppositedirection from the outer periphery to the inner periphery in each of therecording layers from said shallow recording layer to said deepestrecording layer in the shallower order from the light incident sidesurface.

According to another aspect of the present invention of themulti-layer-information-recording medium, predetermined contentinformation related to all contents on said shallow recording layer isrecorded in said deepest recording layer.

According to the present invention, there is also provided aninformation recording and reproducing apparatus capable of recording orreproducing information on either of asingle-layer-information-recording medium having a single recordinglayer and a multi-layer-information-recording medium having a pluralityof recording layers layered on a spacer layer on one side by irradiatinga light beam thereto.

The information recording and reproducing apparatus of the presentinvention comprises:

-   -   an optical pickup having an objective lens which irradiates a        light beam to a multi-layer-information-recording medium which        includes a deepest recording layer disposed deepest from a light        incident side surface at an optical distance d1 satisfying an        equation d1=nt wherein “n” denotes a predetermined refractive        index of the cover layer of the        single-layer-information-recording medium compatible in terms of        at least reproducing and recording with said        multi-layer-information-recording medium and “t” denotes a        thickness of said cover layer, and at least one shallow        recording layer disposed at an optical distance d2 satisfying an        inequality d2<nt from the light incident side surface; and    -   a focus servo circuit which controls the objective lens to,        first of all, focus the light beam to said deepest recording        layer at the optical distance d1, and executes an initial focus        servo operation.

According to one aspect of the present invention of the informationrecording and reproducing apparatus, said focus servo circuit executes afocus servo operation for jumping a focused position to said shallowrecording layer at the optical distance d2 after executing said initialfocus servo operation.

According to another aspect of the present invention of the informationrecording and reproducing apparatus, said objective lens has a numericalaperture equal to or larger than 0.8 for producing a focused spot of thelight beam.

According to a further aspect of the present invention of theinformation recording and reproducing apparatus, the apparatus furthercomprises an wave aberration correcting portion which varies the amountof wave aberration included in said focused spot.

According to a still further aspect of the present invention of theinformation recording and reproducing apparatus, said objective lenscomprises a group of lenses which minimizes the amount of waveaberration in the light beam when the spot is focused at a positionspaced by the optical distance d1.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view schematically showing a two-layer disc;

FIG. 2 is a cross-sectional view schematically showing a single-layerdisc;

FIG. 3 is a cross-sectional view schematically showing a two-layer discaccording to the present invention;

FIG. 4 is a cross-sectional view schematically showing a single-layerdisc which is compatible with the two-layer disc of the presentinvention; and

FIG. 5 is a block diagram for schematically describing the configurationof a recording and reproducing apparatus according to the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, embodiments of the present invention will be described withreference to the accompanying drawings.

Two-Layer Disc

An exemplary multi-layer disc according to a first embodiment of thepresent invention is a two-layer disc having a two-layer structurecomprised of recording layers L1, L2, for example, as shown in FIG. 3.This is a two-layer disc which is compatible in terms of reproduction orrecording with a single-layer disc (FIG. 4) on which reproduction orrecording is performed by a predetermined reproducing or recording meansthrough a cover layer on a recording layer on a light incident sidesurface having a predetermined refractive index n and a thickness t.

The deepest recording layer, i.e., the recording layer positioneddeepest from the light incident side surface of the recording layers ofthe two-layer disc is covered with a cover layer having a thicknesswhich is related to an optical distance d1 as expressed by d1=n×t.

The shallow recording layer, other than the deepest recording layer, iscovered with a cover layer having a thickness which is related to anoptical distance d2 as expressed by d2<n×t. The two-layer disc comprisesthe deepest recording layer formed at the optical distance d1 whichsatisfies the equation d1=n×t, and the shallow recording layer formed atthe optical distance d2 which satisfies the inequality d2<n×t.

In this two-layer disc, since the deepest recording layer is set at theoptical distance d1 at the same position of the optical path thicknessas the recording layer of the single-layer disc, information on thedeepest recording layer at the optical distance d1 can be reproducedwithout searching for the position of the shallower recording layer ofthe multi-layer disc even by a pickup which is adapted to minimize thewave aberration for the single-layer disc. Also, since the opticaldistance d2 is set shorter than d1, an allowance for an inclined disc,when recording or reproducing is performed on the shallow recordinglayer, is not more strict than for the single-layer disc, so that theplanarity need not be improved as compared with the single-layer disc.

With the two-layer disc, information may be recorded on the assumptionthat it is reproduced from the two layers in a predetermined order inwhich the shallow recording layer at the optical distance d2 isreproduced ahead of the deepest recording layer. Specifically, physicaladdress information can be recorded sequentially from the shallowrecording layer to the deepest recording layer, in an order of shallowerlayers from the light incident side surface.

Further, with the two-layer disc, signals are reproduced from the innerperiphery to the outer periphery of the surface at the optical distanced2. Alternatively, signals may be reproduced from the outer periphery tothe inner periphery of the surface at the optical distance d1. Also, thephysical address information can be recorded in order from the innerperiphery to the outer periphery of the deepest recording layer.

By thus designing the two-layer disc, for reproducing a program whichexceeds a recording limit amount of the shallow recording layer,remaining information recorded on the deepest recording layer isreproduced after completion of reproduction from the shallow recordinglayer having a larger allowance for an inclined disc, so that it ispossible to increase the allowance for a normally inclined disc.

In the two-layer disc, predetermined content information related to allcontents on the two layers can be recorded on the deepest recordinglayer at the optical distance d1. In this event, a signal reproducingapparatus reads the title of the two-layer disc, a program recordingtime, or predetermined information indicating that this two-layer discconforms to the opposite track path scheme or the like from the deepestrecording layer at the optical distance d1, and then jumps a focusedposition to the inner periphery of the shallow recording layer at theoptical distance d2 and can continue to reproduce signals. Physicaladdress information may be sequentially recorded alternately in aforward direction from the inner periphery to the outer periphery and inthe opposite direction from the outer periphery to the inner peripheryin each recording layer in the order of depth from the deepest recordinglayer to the shallow recording layer.

With the disc on which information is recorded in the foregoing manner,predetermined information indicative of the content of the disc over twolayers can be read in the same wave aberration correcting state as asingle-layer disc, so that the reproducing apparatus can be aware of atwo-layer disc on which information is recorded without searching forthe position of the recording layers by its wave aberration correctingunit, and can immediately start the reproduction. Thus, according to thepresent invention, when the adjacent recording layers are reproducedfrom the shallow recording layer, the optical pickup can be smoothlymoved between reproducing planes of the recording layers.

This information may be such one that is recorded in an inner peripheralportion of the deepest recording layer as a pit, or a bar code, or whatis called a PEF which forms a bar code like one using pits, or a waveaberration correcting signal for a region in which a signal is recordedfor use in detection of wave aberration in order to correct the waveaberration.

When the numerical aperture of an objective lens for converging a lightspot is chosen to be 0.8 or more, the objective lens is designed tominimize the amount of wave aberration when it focuses through theoptical distance d1.

While the foregoing example has been described for the two-layer disc, adisc having three or more layers can be designed in a similar manner,and other recording layers may also be provided even if they do notsatisfy the foregoing condition. Also, while the recording density hasnot been described, the two recording layers may have the same recordingdensity, or may differ from each other in recording density.

While in the foregoing example, the thickness of the cover layers hasbeen described to be equal in the length of optical path. This can be ofcourse realized by materials equal in the refractive index to each otherand identical in thickness. Otherwise, even with materials havingdifferent refractive indexes, they may be sized to be equal in theproduct of the refractive index and thickness, i.e., the opticalthickness (distance). Also, when a material (spacer) filled betweenlayers has a different refractive index, it can be set to have anequivalent optical path length by sequential calculations.

For example, assuming that the cover layer on the light incident sidesurface of the two-layer disc has a refractive index n_(c) and athickness t_(c), the shallow recording layer L1 has a refractive indexn_(L1) and a thickness t_(L1), and a spacer layer between the recordinglayers L1, L2 has a refractive index n_(s) and a thickness t_(s) thedisc is designed such that the optical distance d1 from the surface onthe light incident side of the deepest recording layer L2 satisfiesd1=n×t=n_(c)×t_(c)+n_(L1)×t_(L1)+n_(s)×t_(s), and the optical distanced2 from the surface on the light incident side of the shallow recordinglayer L1 satisfies d2=n_(c)×t_(c)<n×t.

Each of the recording layers L1, L2 has a laminate structure comprisedof a recording layer made of a phase changing material such asAg—In—Sb—Te, and glass protection layers made of, for example, ZnS—SiO₂or the like which sandwich the recording layer. For an optical discwhich uses a recording layer made of a phase changing material and onwhich data can be recorded or erased, i.e., rewritten using an opticalbeam, each recording layer can be provided with a rewritable region inwhich data can be rewritten, i.e., recorded or erased, and a prepitregion which is provided with trains of emboss pits that carry addressesas sequential physical addresses and information such as recordingtiming. While an example of rewritable two-layer disc using a phasechanging material is described, the material for the recording layer isnot limited to the phase changing material in the present invention, buta write-once pigment material may be used. Moreover, the two-layer discmay be implemented as a disc dedicated to reproduction.

The single-layer and multi-layer discs compatible for reproducing andrecording are common in the disc diameter, overall disc thickness, trackpitch, minimum pitch length, bowing angle, birefringence, format, andthe like, other than the aforementioned conditions. For example, thesemay conform to a CAV (constant angular velocity) or a CLV (constantlinear velocity) scheme. Alternatively, they may be multi-layer disc inaccordance with a zone CAV or a CLV scheme which is a combination of CAVand CLV. In addition, each recording layer of the multi-layer disc ispreviously formed with convex groove tracks and concave groove tracksalternately in a spiral or concentric shape. Each of the groove tracksmay be wobbled at a frequency corresponding to the rotational speed ofthe multi-layer disc.

Recording/Reproducing Apparatus

Data is recorded on the multi-layer disc by irradiating a prepit regionand a rewritable region of a recording layer thereof with a reproducinglight beam having a low intensity (reading power) for scanning to detectland prepits and groove prepits in the prepit region, recognizing theposition on a track to be recorded, and irradiating the rewritableregion of the track with a focused recording light beam (writing power)having a high intensity modulated in accordance with the data.

FIG. 5 is a block diagram illustrating the configuration of a recordingand reproducing apparatus according to the present invention.

An optical pickup 21 comprises an optical system which includes afocusing lens, a beam splitter, an objective lens, and the like; asemiconductor laser which is a light source; a photodetector; anobjective lens actuator; and the like. The objective lens 21a has anumerical aperture equal to or larger than 0.8 and produces a focusedspot of a light beam on a recording layer. The objective lens 21a iscomprised of a group of lenses which minimize the amount of waveaberration of the light beam when either of a compatible single-layer ormulti-layer disc is loaded at a normal position, and when the spot isfocused at the optical distance d1 from the surface. The optical pickup21 comprises a wave aberration correcting means 21b for varying theamount of wave aberration included in the focused spot.

When loading a multi-layer disc 1 onto a turntable 1a driven by aspindle motor, the optical pickup 21 irradiates the multi-layer disc 1with a light beam as recording light or a reading light. The opticalpickup 21 comprises the photodetector which detects a reflected lightbeam from a recording layer of the multi-layer disc to read a signalcorresponding to a track and prepits or recording marks formed on themulti-layer disc 1 as a change in reflectivity. A servo circuit 20 has afocus servo circuit and a tracking servo circuit for performing a servocontrol for focusing and tracking of the pickup, a control for areproduced position (radial position), a control for the rotationalspeed of the spindle motor, and the like based on a control signalprovided from the optical pickup 21 and a control command provided froma control unit (CPU) 26. When the multi-layer disc in the aforementionedexample, for example, a two-layer disc is loaded, the optical beam isfirst irradiated to the deepest recording layer L2 at the opticaldistance d1, executes an initial focus servo operation, and performs atracking servo and a focus servo control for the objective lens suchthat the light beam is focused correctly on the recording layer of themulti-layer disc. The focus servo circuit also executes a focus servooperation for jumping a focused position to the shallow recording layerL1 at the optical distance d2 after executing the initial focus servooperation.

A read signal (RF signal) output from the optical pickup 21 is amplifiedin an amplifier circuit, and supplied to a pre-address decoder 23 and adecoder 43.

The pre-address decoder 23 extracts prepits, wobble signals, and thelike, and a synchronous clock and timing signal generator circuit withinthe pre-address decoder 23 generates a clock signal and a timing signalin synchronism with the rotation of the multi-layer disc 1. The timingsignal represents a current position on the disc such as a prepit regionor a writable region recorded (reproduced) by the light beam, or a landtrack or a groove track or the like. The pre-address decoder 23 readsaddress information from a signal read from emboss pits in the prepitregion of the disc by the pickup, and sends the address information andtiming signal to the CPU 26. The pre-address decoder 23 includes acircuit for detecting the rewritable region and prepit region on themulti-layer disc.

The CPU 26 detects the position of the prepit region on the recordinglayer from these signals. A storage device is contained in or connectedto the CPU 26 for storing necessary data and the like. The CPU 26generally controls the apparatus based on signals supplied thereto. TheCPU 26 reads the address information from the pre-address decoder 23,and sends a control command to a recording control circuit 36 and servocircuit 20 to control a recording and reproducing operation at apredetermined address.

The recording control circuit 36 controls the power of the laser in thepickup in accordance with a particular state such as recording, erasing,reproducing and the like based on a control command from the CPU 26 anda timing signal from the pre-address decoder 23. In a recording state,the recording control circuit 36 modulates the power of the laser in thepickup based on a signal from an encoder 27 to record information on thedisc. In a reproducing state (when data in the rewritable region isreproduced, or when address information in the prepit region isreproduced), the recording control circuit 36 controls the reading powerto maintain at constant low power so as not to erase informationrecorded on the disc.

The encoder 27 adds a parity code for error correction to data to berecorded, and converts the resulting data to an RLL (Run Length Limited)code for encoding to a signal suitable for recording on the multi-layerdisc 1. The encoded signal is sent from the encoder 27 to the recordingcontrol circuit 36.

The decoder 43 performs the processing reverse to that performed in theencoder (demodulation of an RLL code, error correction, and the like) ona signal read from the rewritable region of the disc to recoveroriginally recorded data.

As described above, the present invention provides amulti-layer-information-recording medium which has two or more recordinglayer compatible with a single-layer disc, and a cover layer having thesame optical path length as a cover layer of the single-layer disc, withanother recording layer disposed at the position of a cover layerthinner than that, so that the multi-layer-information-recording mediumexcels in stability for planarity of the disc, and information can berecorded and reproduced in such an order that signals can becontinuously reproduced from these recording layers.

It is understood that the foregoing description and accompanyingdrawings set forth the preferred embodiments of the invention at thepresent time. Various modifications, additions and alternative designswill, of course, become apparent to those skilled in the art in light ofthe foregoing teachings without departing from the spirit and scope ofthe disclosed invention. Thus, it should be appreciated that theinvention is not limited to the disclosed embodiments but may bepracticed within the full scope of the appended claims.

This application is based on a Japanese Patent Application No.2001-156477 which is hereby incorporated by reference.

1. A multi-layer-information-recording medium having a plurality ofrecording layers layered on a spacer layer on one side and adapted to aninformation recording and reproducing apparatus capable of recording orreproducing information on a single-layer-information-recording mediumhaving a single recording layer and a cover layer on one side as achange in reflectivity by irradiating a light beam through the coverlayer onto the recording layer, said multi-layer-information-recordingmedium comprising: a deepest recording layer disposed deepest from alight incident side surface at an optical distance d1 satisfying anequation d1=nt wherein “n” denotes a predetermined refractive index ofthe cover layer of the single-layer-information-recording mediumcompatible in terms of at least reproducing and recording with saidmulti-layer-information-recording medium and “t” denotes a thickness ofsaid cover layer; and at least one shallow recording layer disposed atan optical distance d2 satisfying an inequality d2<nt from the lightincident side surface.
 2. A multi-layer-information-recording mediumaccording to claim 1, wherein said multi-layer-information-recordingmedium consists of said deepest recording layer and said shallowrecording layer as only two layers.
 3. Amulti-layer-information-recording medium according to claim 1, whereinsaid multi-layer-information-recording medium includes physical addressinformation recorded sequentially from said shallow recording layer tosaid deepest recording layer in a shallower order from the lightincident side surface.
 4. A multi-layer-information-recording mediumaccording to claim 1, wherein said multi-layer-information-recordingmedium includes physical address information sequentially recorded inorder from an inner periphery to an outer periphery of said deepestrecording layer.
 5. A multi-layer-information-recording medium accordingto claim 4, wherein said multi-layer-information-recording mediumincludes the physical address information sequentially recordedalternately in a forward direction from the inner periphery to the outerperiphery and in an opposite direction from the outer periphery to theinner periphery in each of the recording layers from said shallowrecording layer to said deepest recording layer in the shallower orderfrom the light incident side surface.
 6. Amulti-layer-information-recording medium according to claim 1, whereinsaid multi-layer-information-recording medium includes predeterminedcontent information related to all contents on said shallow recordinglayer recorded in said deepest recording layer.
 7. An informationrecording and reproducing apparatus capable of recording or reproducinginformation on either of a single-layer-information-recording mediumhaving a single recording layer and a multi-layer-information-recordingmedium having a plurality of recording layers layered on a spacer layeron one side by irradiating a light beam thereto, said informationrecording and reproducing apparatus comprising: an optical pickup havingan objective lens which irradiates a light beam to amulti-layer-information-recording medium which includes a deepestrecording layer disposed deepest from a light incident side surface atan optical distance d1 satisfying an equation d1=nt wherein “n” denotesa predetermined refractive index of the cover layer of thesingle-layer-information-recording medium compatible in terms of atleast reproducing and recording with saidmulti-layer-information-recording medium and “t” denotes a thickness ofsaid cover layer, and at least one shallow recording layer disposed atan optical distance d2 satisfying an inequality d2<nt from the lightincident side surface; and a focus servo circuit which controls theobjective lens to first of all focus the light beam to said deepestrecording layer at the optical distance d1, and executes an initialfocus servo operation.
 8. An information recording and reproducingapparatus according to claim 7, wherein said focus servo circuitexecutes a focus servo operation for jumping a focused position to saidshallow recording layer at the optical distance d2 after executing saidinitial focus servo operation.
 9. An information recording andreproducing apparatus according to claim 7, wherein said objective lenshas a numerical aperture equal to or larger than 0.8 for producing afocused spot of the light beam.
 10. An information recording andreproducing apparatus according to claim 9, further comprising an waveaberration correcting portion which varies the amount of wave aberrationincluded in said focused spot.
 11. An information recording andreproducing apparatus according to claim 9, wherein said objective lenscomprises a group of lenses which minimizes the amount of waveaberration in the light beam when the spot is focused at a positionspaced by the optical distance d1.
 12. Amulti-layer-information-recording medium that is compatible with asingle-layer-information-recording medium in terms of reproducing orrecording, the single-layer-information-recording medium having a coverlayer having a refractive index “n” and a thickness “t” on the lightincident side, said multi-layer-information-recording medium comprisinga first recording layer and a second recording layer that are layered inorder from the light incident side surface of themulti-layer-information-recording medium, wherein the second recordinglayer is disposed at an optical distance “d1” from the light incidentside surface satisfying an equation d1=n×t; and wherein the firstrecording layer is disposed at an optical distance “d2” from the lightincident side surface satisfying an inequality d2<n×t.
 13. Amulti-layer-information-recording medium that is compatible with asingle-layer-information-recording medium in terms of reproducing orrecording, the single-layer-information-recording medium having a coverlayer having a refractive index “n” and a thickness “t” on the lightincident side, said multi-layer-information-recording medium comprisinga cover layer, a first recording layer, a spacer layer, and a secondrecording layer that are layered in order from the light incident sidesurface of the multi-layer-information-recording medium, wherein oncondition that the cover layer has a refractive index “nC” and athickness “tC” and the first recording layer has a refractive index“nL1” and a thickness “tL1” and the spacer layer has a refractive index“nS” and a thickness “tS”, the second recording layer is disposed at anoptical distance “d1” from the light incident side surface satisfying anequation d1=n×t=nC×tC+nL1×tL1+nS×tS; and wherein the first recordinglayer is disposed at an optical distance “d2” from the light incidentside surface satisfying an equation d2=nC×tC<n×t.
 14. Amulti-layer-information-recording medium that is compatible with asingle-layer-information-recording medium in terms of reproducing orrecording, the single-layer-information-recording medium having a coverlayer having a refractive index “n” and a thickness “t” on the lightincident side, said multi-layer-information-recording medium comprisinga deepest recording layer and one or more shallow recording layersshallower than the deepest recording layer that are layered in orderfrom the light incident side surface of themulti-layer-information-recording medium, wherein the deepest recordinglayer is disposed at an optical distance “d1” from the light incidentside surface satisfying an equation d1=n×t; and wherein the shallowrecording layer is disposed at an optical distance “d2” from the lightincident side surface satisfying an inequality d2<n×t.
 15. Amulti-layer-information-recording medium according to claim 14 , whereinsaid multi-layer-information-recording medium consists of said deepestrecording layer and said shallow recording layer as only two layers. 16.An information reproducing apparatus capable of reproducing informationon either of a single-layer-information-recording-medium and amulti-layer-information-recording medium, wherein thesingle-layer-information-recording-medium having a cover layer having arefractive index “n” and a thickness “t” on the light incident side, andwherein said multi-layer-information-recording-medium comprises adeepest recording layer and one or more shallow recording layersshallower than the deepest recording layer that are layered in orderfrom the light incident side surface of themulti-layer-information-recording-medium, and wherein the deepestrecording layer is disposed at an optical distance “d1” from the lightincident side surface satisfying an equation d1=n×t; and wherein theshallow recording layer is disposed at an optical distance “d2” from thelight incident side surface satisfying an inequality d2<n×t; saidinformation reproducing apparatus includes a focus servo circuit thatexecutes an initial focus servo operation first of all for said deepestrecording layer at the optical distance d1.
 17. An informationreproducing apparatus according to claim 16, wherein said focus servocircuit executes a focus servo operation for jumping a focused positionto said shallow recording layer at the optical distance d2 afterexecuting said initial focus servo operation.
 18. An informationreproducing apparatus according to claim 16, further comprising anobjective lens having a numerical aperture equal to or larger than 0.8for producing a focused spot of the light beam.
 19. An informationreproducing apparatus according to claim 18, further comprising a waveaberration correcting portion which varies the amount of wave aberrationincluded in said focused spot.
 20. An information reproducing apparatusaccording to claim 18, wherein said objective lens comprises a group oflenses which minimizes the amount of wave aberration in the light beamwhen the spot is focused at a position spaced by the optical distanced1.
 21. An information recording apparatus capable of recording orreproducing information on either of asingle-layer-information-recording-medium and amulti-layer-information-recording medium, wherein thesingle-layer-information-recording-medium having a cover layer having arefractive index “n” and a thickness “t” on the light incident side, andwherein said multi-layer-information-recording-medium comprises adeepest recording layer and one or more shallow recording layersshallower than the deepest recording layer that are layered in orderfrom the light incident side surface of themulti-layer-information-recording-medium, and wherein the deepestrecording layer is disposed at an optical distance “d1” from the lightincident side surface satisfying an equation d1=n×t; and wherein theshallow recording layer is disposed at an optical distance “d2” from thelight incident side surface satisfying an inequality d2<n×t; saidinformation recording apparatus includes a focus servo circuit thatexecutes an initial focus servo operation first of all for said deepestrecording layer at the optical distance d1.
 22. An information recordingapparatus according to claim 21, wherein said focus servo circuitexecutes a focus servo operation for jumping a focused position to saidshallow recording layer at the optical distance d2 after executing saidinitial focus servo operation.
 23. An information recording apparatusaccording to claim 21, further comprising an objective lens having anumerical aperture equal to or larger than 0.8 for producing a focusedspot of the light beam.
 24. An information recording apparatus accordingto claim 23, further comprising a wave aberration correcting portionwhich varies the amount of wave aberration included in said focusedspot.
 25. An information recording apparatus according to claim 23,wherein said objective lens comprises a group of lenses which minimizesthe amount of wave aberration in the light beam when the spot is focusedat a position spaced by the optical distance d1.
 26. An informationreproducing apparatus for reproducing information from amulti-layer-information-recording medium according to claim 12 .
 27. Aninformation reproducing apparatus for reproducing information from amulti-layer-information-recording medium according to claim 13 .
 28. Aninformation reproducing apparatus for reproducing information from amulti-layer-information-recording medium according to claim 14 .
 29. Aninformation reproducing apparatus for reproducing information from amulti-layer-information-recording medium according to claim 15 .